Production of filaments and fibers have long been known in the art. Typically, these filaments and fibers are produced utilizing well known extrusion techniques. Generally, this includes the use of a single extruder through which a material, such as a polymeric material, is melted and forced through a die head to form the filament.
Filaments which are produced from such single extrusion processes are generally characterized as monofilaments, although the term xe2x80x9cmonofilamentxe2x80x9d has also typically referred to any filaments of indefinite or extreme length. Thus, the term xe2x80x9cmonofilamentsxe2x80x9d as used in connection with single extrusion processes may be more particularly characterized as xe2x80x9cmonoconstitutentxe2x80x9d or monocomponentxe2x80x9d monofilaments, meaning they are extruded from only one polymer and have a homogeneous cross section throughout the entire length of the fiber. For ease of discussion herein, a xe2x80x9cmonofilamentxe2x80x9d will refer to this type of fiber made by this single extrusion process. The term xe2x80x9cfilamentxe2x80x9d will refer to what is often termed xe2x80x9cmonofilamentxe2x80x9d.
Since a single extruder is employed, the processing conditions and parameters, e.g., temperature (heat) profile, screw speed, shear, die size, die profile, draw ratio, etc., can be controlled and manipulated in a manner which can affect the overall physical or mechanical properties of the monofilament thus produced, since it is well known that these processing conditions can and do affect the morphology, i.e., the general shape, arrangement and function of the crystalline structure within the polymer, which in turn influence the properties of the monofilament. However, it will be appreciated that the morphology of the entire monofilament will be substantially the same throughout the entire filament. While the processing conditions and parameters can be controlled and manipulated to affect the final physical properties of the monofilament, the monofilament itself has a morphology which is essentially identical throughout.
Accordingly, in order to obtain better results, various blends of polymers or copolymers have been employed to improve certain desired physical properties of the monofilaments, depending upon the desired application. Traditional applications for monofilament lines include weed trimmer line, fishing line, and sewing threads. These monofilaments may also be woven into or otherwise processed into various industrial and commercial fabrics for various applications including fabrics for use as papermachine clothing, hosiery, and hook and loop fasteners. It will be appreciated that a blend of polymers may provide a different morphology to the monofilament than would a single polymer since the blend has at least one different ingredient. Thus, the mechanical properties of the monofilament comprising a blend of polymers will differ from the mechanical properties of a monofilament comprising a single ingredient.
Although monofilaments have provided suitable results in most applications, the limitations of monofilaments to one material (i.e., either one ingredient or a blend of ingredients) having one general overall morphology has created interest in multi-structural filaments. By the term xe2x80x9cmulti-structural,xe2x80x9d it is meant that, through the cross section of each filament at any place along the length of the filament, there are two or more discrete regions of extruded components. Multi-structural filaments, as known heretofore, are generally referred to as xe2x80x9cmulticomponent monofilamentxe2x80x9d or xe2x80x9ccomposite filamentsxe2x80x9d. These multi-structural filaments are essentially produced by co-extrusion of two or more polymers in such a manner that each polymer occupies a discrete region that runs the length of the filament. When such a filament consists of two discrete materials or polymeric components, the filament is sometimes referred to as a xe2x80x9cbicomponent monofilament.xe2x80x9d The actual shape and size of the discrete regions are predetermined by the extrusion control techniques and die packs employed. Typical multi-structural cross sectional configurations include core-sheath, side-by-side, and islands-in-the-stream configurations. Other, more complex configurations may include core-mantle-sheath configurations, islands-in-the-stream configurations having multiple sized islands or core-sheath configurations where the sheath does not completely surround the core, e.g., core-tips configurations.
Heretofore, multi-structural filaments have been produced as bicomponent or multicomponent filaments utilizing two or more extruders working in tandem to force two or more distinct materials (or distinct blends of materials) through different channels in a common die head so as to produce filaments that contain two or more discrete regions of different materials encompassed in the extruded profiles and determined by way of their respective extruders and die head paths. For instance, to produce a core-sheath bicomponent filament, essentially the same extrusion techniques are utilized as were employed in the production of monofilaments, except that two separate extruders are run in tandem and process two different materials. One extruder is used to melt and force a first ingredient into the die pack which will ultimately produce the core of the filament, while the other extruder is used to melt and force a second, different ingredient into the die pack where it follows a different flow path such that it ultimately produces a sheath around the core in producing the filament.
Because two independently controlled extruders are employed which use two different materials, the characteristics of each of these discrete materials and, therefore, the physical properties within each discrete region of the filament made from one of the materials can be adjusted in a manner which is beneficial to the performance characteristics of the bicomponent filament. For example, suppose one ingredient has excellent abrasion resistance and toughness, but lacks dimensional stability. On the other hand, a second ingredient is not as resistant to abrasion but provides greater dimensional stability. Depending upon the application, it may be beneficial to provide a sheath of the abrasion resistance material around the core component having excellent dimensional stability to provide an improved filament. Thus, it will be appreciated that the use of two extruders and two materials allows for increased versatility of the end product""s physical performance through control of the materials used, control of the processing conditions and the orientation or configuration under which the materials are extruded, sent through the die pack and drawn.
Although bicomponent filaments are becoming increasingly popular, there are still limitations to filament production using the bicomponent process. First and foremost is the issue of compatibility of the components or ingredients. In the example above relating to an ingredient with excellent abrasion resistance and low dimensional stability and a second ingredient with improved dimensional stability but lower abrasion resistance, the first ingredient could be viewed as nylon while the second might be polyethylene terephthalate (PET). However, it is well known that nylon and PET are not sufficiently compatible with each other to produce a bicomponent filament using just these two materials. If nylon were to be made into a sheath around a PET core, without some additional adhesive, compatibilizing agent, or compatibilizing layer therebetween, the filament would simply fall apart as the two are not sufficiently compatible for filament production. In fact, it is known that external stresses or other forces may be sufficient to cause delamination of these incompatible materials, notwithstanding the additives used to keep them together.
Consequently, many patentees and users of the bicomponent process employ materials that, while similar and compatible, are different in terms of their chemical structure or are blends or copolymers of other processing materials. For example, U.S. Pat. No. 6,207,276 discloses a core-sheath bicomponent fiber wherein the core is produced from nylon 6 or nylon 6,6, while the sheath is produced from polyamides having a melting point of at least 280xc2x0 C., such as nylon 4,6, 9T, 10T, 12T, or nylon copolymers 46/4T, 66/6T, and 6T/6I. These latter nylon homopolymers and copolymers, as well as their base monomers, are very different in their morphologies from nylon 6 or nylon 6,6 and their base monomers.
Similarly, U.S. Pat. No. 4,069,363 discloses a bicomponent filament wherein the core is produced as a copolymer of hexamethylene dodecanedioamide (i.e., nylon 6,12) and E-caproamide (i.e., nylon 6), while the sheath is either nylon 6,12, nylon 6,6 or nylon 6 only. Again, the starting materials employed prior to extrusion are not the same and have different chemical structures, morphologies, and physical properties prior to being extruded.
Still other examples of bicomponent processes include U.S. Pat. No. 5,948,529 wherein a bicomponent filament having a core of PET and sheath of polyethylene is disclosed. The PET core also includes a functionalized ethylene copolymer blended therein. Clearly, the morphologies of the core and sheath starting components in this patent differ greatly.
U.S. Pat. No. 6,254,987 discloses a core-sheath bicomponent filament which displays enhanced abrasion resistance. The core is a liquid crystalline polyester and the sheath is a blend of 1 to 5 percent by weight polycarbonate and a polyester. Again, the core and sheath starting materials are different in chemical structure.
Also, U.S. Pat. No. 5,540,992 discloses a bicomponent fiber comprising a high melting core comprising high density polyethylene and a low melting sheath comprising low density polyethylene. Thus, while the fiber contains the class of polymers (i.e., polyethylene) in both the core and the sheath, it does not contain the same ingredient having the same chemical structure and physical morphology. That is, the chemical structure, molecular weight and molecular weight distribution, among other things, are different between the core component and the sheath component prior to extrusion. In other words, low density polyethethylene and high density polyethylene, while having similar chemical composition, are quite different in morphology and topology.
Thus, heretofore, the prior art has not envisioned using the same ingredient for producing all structural parts or discrete regions of a multi-structural filament. Unexpectedly, it has been discovered that by controlling the extrusion process control profiles and the shear rate of the ingredients as they are processed, different morphologies of the same ingredients can be produced to provide structural parts or discrete regions of a filament with beneficial properties.
Before proceeding however, U.S. Pat. No. 3,650,884 is noted. This patent discloses a polyamide monofilament having a diameter of at least 15 mils and a microporous surface layer having a thickness of about 3 to 15 microns constituting less than 6 percent of the transverse radius of the monofilament. While the monofilament is truly a monoconstitutent monofilament (i.e., not a multi-structural filament) in that it is extruded from a single extruder containing one material, i.e., polyamide, the resultant morphology of the very thin surface layer after complete processing does differ from that of the rest of the monofilament once it has been subjected to the steaming and drawing processes set forth in the patent. This steam disoriented surface layer is, in reality, only a skin layer and constitutes less than 6 percent of the filament. In contrast, each structural profile or region created by the extrusion of the parts of a filament through the die pack necessarily constitutes more than 7 percent, and preferably more than 10 percent, of each filament where multi-structural filaments are produced using known co-extrusion techniques. Thus, it will be appreciated that the monofilament produced in U.S. Pat. No. 3,650,884 differs considerably from the multi-structural filaments produced using bicomponent processing techniques and extrusion techniques of the present invention.
Thus, the need exists for an extruded, multi-structural filament comprising only one single ingredient and having increased physical properties and performance due to the control of the shear, melt temperature, and other well known processing conditions during extrusion through a die pack.
The present invention generally relates a multi-structural filament wherein each discrete region (e.g., core, sheath, etc.) of the filament is made from the same ingredient but has a different morphology from any other different region extruded in tandem therewith after processing. Thus, the present invention preferably uses a single ingredient in two or more extruders to form a multi-structural filament having improved physical properties as compared to monofilaments and, in some instances, as compared to bicomponent filaments. It will be appreciated that some parts of the filament may have the same morphology where the processing conditions have been preset to be substantially the same. Thus, in a filament having a core-sheath cross-sectional configuration where the sheath does not completely surround the core, each portion of the sheath may have the same morphology as every other region denoted as the sheath, provided such processing is desired. Thus, as used hereinafter, each xe2x80x9cregionxe2x80x9d shall refer to the discrete parts of the filament having the same morphology, while the term xe2x80x9cpartsxe2x80x9d may refer to each portion of the filament individually.
More particularly, the present invention generally provides a multi-structural filament comprising a single ingredient having two or more morphologies after extrusion through a die pack wherein one discrete region of the filament comprises one morphology of the ingredient and at least another discrete region of the filament comprises another morphology of the same ingredient, and wherein each region of the filament comprises at least about 7 percent of the filament.
By the term xe2x80x9csingle ingredient,xe2x80x9d it is meant that the initial starting materials employed in the extruders are essentially chemically and physically identical. Where homopolymers and commercially available resins are directly employed, this means that the initial starting materials have the same chemical structure, and essentially the same molecular weight, molecular weight distribution, extractables, melting point, melt viscosity, and melt flow. Thus, a low density polyethylene and a high density polyethylene would not be a xe2x80x9csingle ingredient.xe2x80x9d Where blends or copolymers are employed, this means that the monomers or starting components employed are the same. However, it will be understood that monomer ratios and blend ratios in the copolymers and blends, respectively, might vary slightly, up to about 20 percent, more preferably, within about 10 percent, and even more preferably, within about 2 percent of each other, without departing from the scope of the invention with respect to the definition of xe2x80x9csingle ingredient.xe2x80x9d Thus, a copolymer having a 90:10 monomer ratio in one extruder would be considered the same xe2x80x9csingle ingredientxe2x80x9d if the other extruder were to use the same monomers in an about 70:30 ratio, and more preferably, in an about 80:20 monomer ratio. Blend ratios would also be recognized in this way so long as the initial ingredients were the same, i.e., identical. Wider ratios of monomers or material blends could also be suitable provided they do not affect the essential nature of the inventionxe2x80x94that is, the morphologies (i.e., the crystallinity) of the copolymers are essentially the same. In some instances, it is possible that monomer ratios or blend ratios of less than 20 percent by weight will not be suitable where the morphologies of the compositions prior to extrusion are affected by the difference in the ratios. It will be appreciated, however, that one of ordinary skill in the art will be able to readily determine what morphologies are affected without any undue experimentation, it being evident that one of ordinary skill in the art should not be able to vary the monomer ratios or blend rations in so small of an amount as to not produce any effective difference in the copolymer or blend.
Advantageously, the present invention allows for a more versatile end product, i.e., a multi-structural filament, having improved physical properties and performance characteristics. In essence, the invention provides for a toughened, more abrasion resistant composition in at least one part of the filament which is certainly compatible with any other part of the filament since it is the same ingredient. Thus, the filament improves certain physical characteristics while maintaining other characteristics found in the ingredient employed without resorting to blends of more than one ingredient in the construction of the filament. This will advantageously reduce costs required in using two or more separate and distinct ingredients.